The internal structure of a battery, both before and after the charging process, is already known. Now, a team of scientists led by the Technical University of Munich has determined, for the first time, the internal workings of batteries during charging and discharging. They observed a battery’s lithium distribution during the entire charging and discharging process.
Lithium ions move from the cathode to the anode during charging. During discharging, they move from the anode to the cathode. In their study, scientists used the materials science diffractometer STRESS-SPEC to observe the lithium distribution. They then verified the measurements using the high-resolution powder diffractometer SPODI.
The scientists discovered that lithium distribution constantly varies during charging and discharging.
Dr. Anatoliy Senyshyn from the Technical University of Munich’s Research Neutron Source Heinz Maier-Leibnitz (FRM II) said, “When the lithium is unevenly distributed, the exchange of lithium between the anode and the cathode doesn’t work at hundred percent in the parts of the battery where too much or too little lithium is present. However, an even distribution of lithium increases performance.”
Scientists also captured the uneven distribution of lithium in a battery with high-resolution images. They obtained the situation in the entire battery by investigating one small partial volume after another and put these individual images together to form an overall picture.
Scientists were able to choose partial volumes with dimensions on the order of micrometers with the support of the Helmholtz Association’s DESY (“Deutsches Elektronen-Synchrotron”) and the European Synchrotron Radiation Facility ESRF. As a result, the scientists found that lithium is irregularly distributed along with the electrode layers and perpendicular to them.
Senshyn said, “The effects observed may help in the long-term development of rechargeable batteries, for example, for electric cars. The distribution of lithium can influence many battery properties. Once we have these better under control, we’ll be able to significantly improve the performance of batteries in the future.”
- Dominik Petz et al. Lithium distribution and transfer in high-power 18650-type Li-ion cells at multiple length scales. DOI: 10.1016/j.ensm.2021.06.028